The first year, I listed my pass fail classes as P/F... They changed them to S/U
The next year, I listed them as S/U so they wouldn't change them... They changed them to P/F.
The third year, I listed them as P/F... They left them as P/F... "THANK YOU AAMC!"
Also, I was an engineer so some of my classes could be MBPC or other. The first year, I put alot as MBCP... No problems.. The second year, I stupidly (it was on the computer and looked like I needed to put them as other) put them as other... Then the third year, I decided I was stupid and put them into the science courses where I felt they belonged. No body complained the first, second, or third year.
Hope that helps. If you correctly put it in this year, they will simply see that you made an honest mistake last year... IF anybody even notices or cares... Last year is over. It's fixed for this year and that is the year they care about.